export function b64ToUint6(nChr: number) {
  return nChr > 64 && nChr < 91
    ? nChr - 65
    : nChr > 96 && nChr < 123
    ? nChr - 71
    : nChr > 47 && nChr < 58
    ? nChr + 4
    : nChr === 43
    ? 62
    : nChr === 47
    ? 63
    : 0
}

// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding
export function base64DecToArr(sBase64: string, nBlocksSize: number) {
  const sB64Enc = sBase64.replace(/[^A-Za-z0-9+/]/g, '')
  const nInLen = sB64Enc.length
  const nOutLen = nBlocksSize
    ? Math.ceil(((nInLen * 3 + 1) >> 2) / nBlocksSize) * nBlocksSize
    : (nInLen * 3 + 1) >> 2
  const taBytes = new Uint8Array(nOutLen)

  let nMod3
  let nMod4
  let nUint24 = 0
  let nOutIdx = 0
  for (let nInIdx = 0; nInIdx < nInLen; nInIdx++) {
    nMod4 = nInIdx & 3
    nUint24 |= b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << (18 - 6 * nMod4)
    if (nMod4 === 3 || nInLen - nInIdx === 1) {
      for (nMod3 = 0; nMod3 < 3 && nOutIdx < nOutLen; nMod3++, nOutIdx++) {
        taBytes[nOutIdx] = (nUint24 >>> ((16 >>> nMod3) & 24)) & 255
      }
      nUint24 = 0
    }
  }

  return taBytes
}
